I am in paper-writing mode, which means (among other trials and tribulations) I am wrestling with the issue of tense. Specifically, did I apply my methods in the past, or am I implementing them now? Did my results show something, or are they still showing them? Which tenses need to match (and when…)?
Primarily, this is a matter of style, and there seems to be a consensus that the present tense is somehow indicative of more exciting, more relevant results. Start your paper ‘Here, we show for the first time…’ and you are right on the bleeding tip of the cutting edge. ‘Here, we showed for the first time…’, on the other hand, and you are already yesterday’s news.

Now, I’ll plead guilty to sprucing up my dry academic prose with liberal sprinklings of immediacy, probably more often than is strictly healthy. But this kind of perky presence can really grate if used to excess, and can lead one into tricky little linguistic culs de sac to boot. A special bugbear of mine, for instance, is the insistence of all TV and radio historians on relating long-past events exclusively in the present tense. “In 1066, William invades England. After a bloody battle, he is victorious…”, and suchlike. I assume they have all been told that it somehow brings history alive to talk in this way. It didn’t, it doesn’t, and it won’t. It just annoys me. (If you’ve never noticed this before, you will now, and I’m afraid I may have ruined your enjoyment of the otherwise wonderful Simon Schama, for which I apologise!)

To return to the matter in hand, the particular problem with writing, say, a description of your statistical methods in the present tense, is what happens when one thing leads to another? For example, suppose you fit(ted) a linear model to some data, but on inspection of the model output, decide to remove a non-signficant interaction in order to make interpretation easier. You could find yourself writing:

“We model y as a function of x1, x2, and their interaction. Because the interaction is not significant, we exclude it and re-run the model”, which doesn’t seem right to me – you have described a sequence of events, but only one point in time. But if you start with “We modelled y as a function of x1, x2, and their interaction…” you are then committed to the past tense throughout.

Similar choices have to be made in the results. Is y significantly related to x; or was it? I tend to prefer the present in this case, because to use the past tense implies that the results were somehow contingent on something specific I did on the single occasion I ran the models for the paper, rather than being a constant property of the data (analysed according to my protocol).

But consistency is the key. And with a large pool of co-authors, and sufficient iterations of a manuscript through multiple drafts, tenses do tend to drift. So you can be performing an experiment which produced certain results, and other logical slips.

None of this really matters, perhaps. But if you want reading your paper to be a pleasant experience (as well as a necessary one, naturally) for your peers, then maybe it is worth plotting the timeline of your sentences to make sure no wormholes have appeared.

(For more on scientific writing, by the way, Tine Janssens has collected a load of good links in her latest interesting post, so rather than replicate them here, I’d encourage you to read them there.)